So we have removed LUN from powerpath.
If you want your system to be "clean" from unused scsci block devices then you should remove scsi block devices that were associated with removed LUN.

#cd /sys/block/sdba/device
if you list content of this folder you will see delete file.

#echo 1 > delete

will delete sdba scsi block device from system.

To release emcpowern block device do this

# powermt release

If you don't release emcpower (in are case emcpowern) block device, next time when you add new LUN it wont't use letter r because system see that emcpowerr device as used. It will have letter o.
You should repeat this step for rest of scsi block devices associating with removed LUN.